Bottom Bracket Gearshift With High-Speed Input Stage for Compact E-Bikes
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Solution Overview
Problem
Existing electric bicycles with bottom bracket gearshifts face challenges in combining an auxiliary drive due to space constraints and weight distribution issues, as traditional gear systems are either high-maintenance and bulky or excessively heavy when positioned at the rear wheel.
Innovation Solution
A bottom bracket gearshift design featuring a high-speed input stage with a transmission ratio between 3:1 and 5:1, which reduces torque requirements, allowing for smaller and lighter gears, and includes a freewheel mechanism to prevent the auxiliary drive from engaging when pedaling stops, along with a coaxial hollow shaft for improved design flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If a traditional derailleur gear system is used at the bottom bracket, then the gearshift components are accessible and easy to maintain, but the system becomes high-maintenance due to contamination from unprotected components
Solution Approach 1:
The patent merges the gearshift system with the bottom bracket auxiliary drive into a single integrated unit. The gearshift components are housed within the same structure as the motor, creating a unified system that is both protected and maintainable through the common access points of the bottom bracket assembly.
Solution Approach 2:
The bottom bracket assembly serves multiple functions: it houses the auxiliary motor, contains the gearshift mechanism, and provides structural support for the bicycle frame. This multi-functional design consolidates what would traditionally be separate components into a single maintainable unit.
2Reliability
If a hub gear is used on the rear wheel, then the gearshift is encapsulated and maintenance-free, but the weight distribution becomes unfavorable with high weight on the rear wheel
Solution Approach 1:
The patent combines the gearshift mechanism with the bottom bracket auxiliary drive, relocating the enclosed gear system from the rear wheel hub to the bottom bracket area. This integration maintains the protective enclosure of hub gears while redistributing weight to achieve better balance on the bicycle frame.
Solution Approach 2:
The invention moves the gearshift system from a horizontal distribution (rear wheel) to a central vertical position (bottom bracket), changing the spatial dimension of weight distribution. This allows the enclosed gear mechanism to be positioned centrally rather than at the extreme rear, improving weight balance.
3Weight of moving object
If a bottom bracket gearshift is used, then the weight distribution is favorable with central positioning, but the installation space is insufficient due to the large size of traditional gearshifts
Solution Approach 1:
The gearshift mechanism is nested within the housing of the bottom bracket auxiliary drive. The gear components are arranged concentrically and axially within the limited space of the motor housing, allowing the gearshift to be contained within the volume already required for the motor assembly.
Solution Approach 2:
The patent employs a high-speed input stage with a transmission ratio of 3:1 to 5:1, which reduces the torque requirements and allows for smaller, lighter gear components. This parameter change in the transmission ratio enables miniaturization of the gearshift mechanism to fit within the constrained bottom bracket space.
4Weight of moving object
If the auxiliary drive is integrated at the bottom bracket, then the weight distribution improves, but the space available for the motor is reduced due to the presence of the gearshift
Solution Approach 1:
The auxiliary motor and gearshift mechanism are merged into a single integrated bottom bracket assembly. The motor housing serves as the housing for the gearshift components, eliminating the need for separate spaces for each component and allowing both functions to coexist within the same volume.
Solution Approach 2:
The gearshift components are nested within the motor housing structure. The planetary gears, input shaft, and related components are arranged within the cylindrical volume of the motor assembly, effectively utilizing the available space without requiring additional volume beyond what the motor already occupies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design achieves a favorable weight distribution by reducing the overall weight of the gearshift while maintaining efficient power transmission, enabling the integration of an auxiliary drive at the bottom bracket without increasing the bicycle's weight excessively.
Implementation Method 1
an input stage, the input stage being arranged between the bottom bracket shaft and the gearbox and being configured as a transmission into high-speed
Implementation Method 2
a freewheel mechanism to prevent the auxiliary drive from engaging when pedaling stops
Data Source
AI summary
Presented herein is a bottom bracket gearshift (1) of an electric bicycle (64) with an auxiliary drive (22), in particular in the form of a central motor. The bottom bracket gearshift (1) has a shift gearbox (4). In order to make the shift gearbox as small and light as possible, an input stage (14) is arranged at the transmission input (10) of the shift gearbox (4). The input stage (14) may be arranged between a bottom bracket shaft (6) and/or the auxiliary drive (22) and is configured as a transmission into high-speed.